Background
With the continuous development of the industry in China, the demand of the society on electric power is greatly increased, and the demand on large-scale generators is directly increased. The operation stability of the generator is greatly influenced by insulation, and particularly, an obvious electric field concentration phenomenon appears at the end part of a stator bar of the generator, and is mainly represented by corona discharge. In order to make the electric field distribution on the surface of the motor bar uniform, various influencing factors, such as the length of each section of anti-corona layer, the resistivity of each section of anti-corona layer material and the like, need to be considered during design, and the correct adjustment of the matching among the various factors is the key for improving the insulation performance of the motor bar.
In the production process of the stator bar of the generator, the motors with different installed capacities need to be designed in a targeted mode. The insulation performance of the winding bar is influenced by various factors, such as selection of main insulation and anti-corona layer materials of the motor winding bar, the length of each segment of the segmented anti-corona structure, the lap joint length between the two segments, the thickness of the main insulation and the anti-corona layer, and the like.
Aiming at the problems, the invention provides a multi-factor optimization design method for the surface electric field of the motor bar, and the multi-factor optimization is carried out on the motor bar through a composite algorithm combining a neural network and a genetic algorithm, so that the modeling time is short, the material cost of equipment is saved, and the risk and the error of manual operation are reduced.
Disclosure of Invention
The invention aims to provide a multi-factor optimal design method for a surface electric field of a motor winding bar, which is used for obtaining a multi-factor optimal matching scheme of the motor winding bar design and solving the problems of high cost, high risk, long period, low efficiency and the like of an entity test.
The multi-factor optimization design method for the surface electric field of the motor bar comprises the following steps:
(1) the method comprises the steps of collecting existing stator bar structure distribution data and the maximum tangential electric field intensity of the surface of a corresponding bar as a training data set, and reserving 10 groups of data as a test set of model accuracy. The distribution data of the stator bar is the length of each section of the anti-corona layer, the conductivity of the anti-corona layer, and the corresponding performance evaluation data is the maximum tangential electric field intensity on the surface of the bar. The relationship between the maximum tangential electric field intensity and the length and the conductivity of the anti-corona layer can be obtained by a finite element simulation result of the end part of the motor wire rod.
(2) A random number function randderm in matlab is used to generate a random number sequence for randomly sampling the training set samples.
(3) Creating a network structure according to the BP neural network, and calling to create a network net (newff (p _ train, t _ train, n), wherein the p _ train distributes data for the stator bar structure in the selected data set, the t _ train is the maximum tangential electric field intensity in the selected data set, and the n is the number of hidden layers. And a three-layer network structure is arranged, wherein 12 layers are arranged on the hidden layer, so that the model precision can be effectively improved.
(4) And (3) calling a matlab neural network tool box train (net, p _ train, t _ train) network to train by using the training set data randomly selected in the step (2), wherein the net is the initial neural network created in the step (3). The trained neural network model can enable the distribution data of the anti-corona layer of the motor bar and the corresponding maximum tangential electric field intensity to establish a multi-input single-output mapping relation.
(5) Preventing corona according to each section collected in (1)And taking the maximum value and the minimum value of the anti-corona layer data of each section as a data range. Since the conductivity changes are between orders of magnitude, log is taken of all conductivity data10. Converting the logarithm of the maximum value of the length of each anti-corona layer and the maximum value of the conductivity into binary numbers, summing the binary numbers to serve as the DNA sequence length of the individuals in the genetic algorithm, and generating 100 individuals with the DNA length by using a rand function to form an initial population of the genetic algorithm.
(6) And calling the trained neural network structure by using matlab statements sim (net, E) as a fitness function of the genetic algorithm, wherein the output is the maximum tangential electric field intensity corresponding to E, and the fitness function is used for calculating the fitness value of all individuals in the population, wherein X is ═ decimal anti-corona layer length decimal anti-corona layer resistivity.
(7) Selecting the current population according to a fitness function, eliminating individuals with low fitness (namely individuals with low evaluation on the performance of the wire rod), reserving excellent individuals, exchanging binary numbers of the same position in DNA of two adjacent excellent individuals as a cross process, and randomly negating or reserving the binary number of each position as a variation process, thereby generating the next individual.
(8) And (5) repeating the operation of the step (7) until individuals with the maximum electric field intensity below 1.5kV/cm are generated, and ending the genetic algorithm.
The invention has the beneficial effects that: 1. the advantages of the neural network are fully utilized, and the function relationship which is difficult to quantify between various design factors and performance requirements is established by using a network form; 2. the invention overcomes the defects of high cost, long period, low efficiency and the like of the entity test;
Detailed Description
The invention is further illustrated by the following examples, which are not to be construed as limiting the invention.
Fig. 1 shows a flowchart of a multi-factor optimization design method for a surface electric field of a motor bar, which is described by taking an example of optimization of an end part structure of a stator bar of a hydraulic generator with a rated voltage of 24kV and a rated capacity of 1000MW as an example:
step S1, selecting an optimization objective, obtaining an initial training data set:
the optimization target in the embodiment is to adjust the medium resistance length, the medium resistance resistivity and the high resistance resistivity of the corona prevention layer of the motor bar so that the maximum tangential electric field on the surface of the motor bar is lower than 1.5 kV/cm. Establishing a sample set (X) by combining a finite element simulation model of the end part of the electrode wire rodi,Yi) 1, 2., N }, where X represents an input item of the mapping, Y represents an output item of the mapping, and the input items are medium resistance length, medium resistance resistivity, and the output item is electric field strength. The sample size N is 100, with 90 sets being the training data set and 10 sets being the test set.
Step S2, normalization processing:
because the magnitude of the selected training set parameters is greatly different, the training set and the test set are normalized, and the normalization processing formula is as follows:
step S3, establishing a neural network structure:
the MATLAB neural network tool box is set into a three-layer network structure comprising an input layer, a hidden layer, a data layer and a data layer,And outputting the layer, wherein the hidden layer is provided with 12 nodes. The training times can be adjusted according to the accuracy of the training result, the initial setting is 1000 times, the learning rate is set to 0.01, and the training mean square error is set to 10-5。
Step S4, training the network, evaluating the accuracy of the neural network:
training a neural network by using a MATLAB tool box, calling to create a netword net (X, Y,12), inputting normalized training set data into the neural network, and calling a MATLAB neural network tool box train (net, X, Y) network for training. And (3) putting 10 groups of input items in the test set into the neural network, comparing the output obtained by calculating the neural network with the electric field intensity corresponding to the test set, and verifying the accuracy of network calculation, wherein the calculation accuracy of the neural network is higher as can be seen from fig. 2.
Step S5, initializing the genetic algorithm initial population:
and taking the maximum value and the minimum value of each section of anti-corona layer data as a data range according to the data of the medium resistance length, the medium resistance resistivity and the high resistance resistivity of 100 groups of motor bar anti-corona layers in S1. Since the conductivity changes are between orders of magnitude, log is taken of all conductivity data10. Converting the logarithm of the maximum value of the length of each anti-corona layer and the maximum value of the conductivity into binary numbers, summing the binary numbers to serve as the DNA sequence length of the individuals in the genetic algorithm, and generating 100 individuals with the DNA length by using a rand function to form an initial population of the genetic algorithm. The population size is set to 100.
Step S6, constructing a fitness function, and evaluating individual fitness:
using matlab statement sim (net, E) to call the trained neural network structure as the fitness function of the genetic algorithm, wherein the output is the maximum tangential electric field intensity corresponding to X, and the maximum tangential electric field intensity is used for calculating the electric field intensity corresponding to all individuals in the population, wherein E is [ length of middle-resistance anti-corona layer, length log of middle-resistance anti-corona layer, and length log of high-resistance anti-corona layer10(medium resistivity) log10(middle and high resistivity)]. Outputting the electric field intensity according to the parameter data carried by the individual, and the individual fitness with smaller electric field intensityHigher. In order to be matched with the use of the neural network, when the fitness of an individual is calculated, each segment of the DNA binary code of the individual is converted into decimal data, and then an sim statement is input.
Step S7, genetic manipulation, generating next generation individuals:
based on individual fitness, selecting excellent individuals, eliminating individuals with low fitness, exchanging binary numbers of two adjacent excellent individuals at the same position to be used as a cross process, and randomly negating or reserving the binary number at each position to be used as a variation process, thereby generating the next individual.
Step S8, generating an optimization result:
and repeating the steps S7 and S8 until the population of a certain generation obtains the maximum fitness, namely the minimum electric field strength meets the optimization standard, ending the genetic optimization process, and obtaining the data of the middle resistance length, the middle resistance resistivity and the high resistance resistivity of the corona prevention layer of the optimal motor bar and the corresponding maximum electric field strength.
The invention can obtain the optimal optimization scheme of the motor bar structure design, randomly extracts 5 groups of motor bar structure design schemes (see figure 6), and compares the optimal scheme with the optimization scheme (see figure 7), and the maximum electric field of the optimization result is the lowest value as can be seen from figure 3, thus proving that the optimization effect is better. Fig. 4 and 5 show simulation diagrams of the tangential electric field and the electric potential of the surface of the bar corresponding to the optimal optimization scheme, and it can be seen that the uniformity of the electric field distribution is better and the maximum electric field intensity is lower.
In the description herein, references to the terms "one embodiment" or "an embodiment" mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above do not necessarily refer to the same embodiment or example.
The above examples represent several embodiments of the present invention, and the description thereof is more specific and detailed, but not to be construed as limiting the scope of the present invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.